Aromatase and seladin-1 are enzymes that have major roles in estrogen synthesis and are important in both brain physiology and pathology. Aromatase is the key enzyme that catalyzes estrogen biosynthesis from androgen precursors and regulates the brain’s neurosteroidogenic activity. Seladin-1 is the enzyme that catalyzes the last step in the biosynthesis of cholesterol, the precursor of all hormones, from desmosterol. Studies indicated that seladin-1 is a downstream mediator of the neuroprotective activity of estrogen. Recently, we also showed that there is an interaction between aromatase and seladin-1 in the brain. Therefore, the expression of local brain aromatase and seladin-1 is important, as they produce neuroactive steroids in the brain for the protection of neuronal damage. Increasing steroid biosynthesis specifically in the central nervous system (CNS) without affecting peripheral hormone levels may be possible by manipulating brain-specific promoters of steroidogenic enzymes. This review emphasizes that local estrogen, rather than plasma estrogen, may be responsible for estrogens’ protective effects in the brain. Therefore, the roles of aromatase and seladin-1 and their interactions in neurodegenerative events such as Alzheimer’s disease (AD), ischemia/reperfusion injury (stroke), and epilepsy are also discussed in this review.

There is still no approved treatment for Alzheimer’s disease (AD), a progressive neurodegenerative disorder characterized by amyloid plaques, neurofibrillary tangles, and synaptic dysfunction. In an in vitro AD model, this study aimed to comparatively assess the neuroprotective effects of the citrus flavonoid Hesperidin and the casein kinase 2 (CK2) inhibitor 5,6-dichloro-1-β-D-ribofuranosyl benzimidazole (DRB) as potential therapeutic targets for AD. First, SH-SY5Y neuroblastoma cells were differentiated into cholinergic neuron-like cells using all-trans retinoic acid (RA) and brain-derived neurotrophic factor (BDNF). Then, to generate an in vitro AD model, 20 μM Aβ_1–42 was applied to induce neurotoxicity in differentiated SH-SY5Y cells. The neuroprotective effects of the CK2 inhibitor DRB and Hesperidin on the in vitro AD model were evaluated using MTT, RT-qPCR, and ELISA methods. Both Hesperidin and DRB, at high concentrations, reduced cell viability in differentiated SH-SY5Y cells for 24 and 48 h (p < 0.05 to p < 0.01). Pre-treatment with Hesperidin at 25 and 50 µM and DRB at 0.25 and 0.5 µM for 24 h increased ADAM10 gene expression and decreased BACE1 gene expression, both of which are associated with AD markers, compared to the 20 µM Aβ_1-42 treatment group (p < 0.05). Pre-treatment with the DRB at 0.25 and 0.5 µM concentrations for 24 h decreased CK2α gene expression in the in vitro AD model compared to the 20 µM Aβ_1-42 treatment group (p < 0.05), whereas Hesperidin had no effect (p > 0.05). Both pre-treatment with Hesperidin and DRB significantly decreased Aβ_1-42 levels (p < 0.01), p-Tau (T181) levels (p < 0.05), and the Bax/Bcl-2 ratio (p < 0.05). As a result, our study showed that both Hesperidin and DRB inhibited Aβ production by suppressing the amyloidogenic pathway and activating the non-amyloidogenic pathway while also exerting an inhibitory effect on neuronal apoptosis. CK2 may be a potential therapeutic target and could contribute to the pathophysiology of AD. However, these findings should be validated by further studies.